Two-shell axial-plane split casing structure for high-capacity low-pressure sections of a steam turbine

ABSTRACT

A steam turbine casing for a high-capacity low-pressure section of two-shell construction divided along an axial plane comprises an inner casing in the form of a guide blade carrier to which the guide blades are attached and an outer casing provided with a thermally-resilient lead-through for a steam inlet pipe. The inner casing is constructed from three frustum-shaped shells arranged approximately normal to each other and in the region of the steam inlet pipe are joined to a cylindrical shell through which the steam inlet pipe passes. The inner casing is supported by axially-divided rings fixed respectively to the circumference at the ends of the frustum-shaped shells which have the smaller diameter.

United States Patent Brandstitter Oct. 28, 1975 [54] TWO-SHELL AXIAL-PLANE SPLIT CASING 3,773,431 11/1973 Bellati et a1 415/219 R STRUCTURE FOR HIGH'CAPACITY FOREIGN PATENTS OR APPLICATIONS IIjOW'PRESSURE SECTIONS OF A STEAM 433,796 8/1935 United Kingdom 415/219 R URBINE 1,073,519 6/1967 United Kingdom 415/103 Inventor: Kurt Brandstatter Mannheim Italy Germany Primary Examiner-Henry F. Raduazo [73] Asslgnee' Brown Bevel-l Company Attorney, Agent, or Firm-Pierce, Scheffler & Parker Limited, Baden, Switzerland [22] Filed: Sept. 5, 1974 57 ABSTRACT [21] Appl. No.: 503,386 A steam turbine casing for a high-capacity lowpressure section of two-shell construction divided along an axial plane comprises an inner casing in the [30] Foreign Apphc'atlon Pnonty Data form of a guide blade carrier to which the guide Oct. 16, 1973 SwItzerland 14646/73 blades are attached and an outer casing provided with a thermally-resilient lead-through for a steam inlet [52] 415M003 HS/103; 415/219 R pipe. The inner casing is constructed from three frus- [51] Int. Cl. F01D 3/02 tum shaped Shells arranged approximately normal to Field Of Search each other and in the gi of the Steam inlet 415/219 108 are joined to a cylindrical shell through which the steam inlet pipe passes. The inner casing is supported [56] References C'ted by axially-divided rings fixed respectively to the cir- U TE STATES PATENTS cumference at the ends of the frustum-shaped shells 2,367,134 1 1945 Mierley 415 219 R which have the smaller diameter. 3,529,901 9/1970 Hart et al 4l5/l03 6 Cl 1 D F. 3,594,095 7/1971 Trassel et al 415/108 "awmg TWO-SHELL AXIAL-PLANE SPLIT CASING STRUCTURE FOR HIGH-CAPACITY LOW-PRESSURE SECTIONS OF A STEAM TURBINE This invention relates to an improvement in a steam turbine casing for high-capacity low-pressure sections of two-shell construction divided on an axial plane, comprising an inner casing in the form of a guide-blade carrier to which the guide blades are attached, and an outer casing provided with thermally resilient leadthroughs for the steam pipe.

Steam turbine casings are known in which the inner casing comprises essentially a number of annular discs arranged in radial planes and divided on an axial plane and which act as supporting elements. The annular discs are supported with respect to each other, at the outer circumference, by means of cylindrical shell plates, and at the inner circumference by struts or bracing plates arranged parallel to the blade passage. Between the annular discs and the outer shell are chambers which are used for the extraction points for the various stages.

A further known technique in the case of steam turbine casings for low-pressure sections is to fit the inner casing with an internal casing structure for part of the guide blading, such that the inner casing can be considered as containing another inner casing.

The disadvantages of the known types of construction lie in the relatively high cost of manufacture due to the different kinds of struts and bracing plates, and the difficulty of adjusting and aligning the inner casing during erection and in service. Since the parts of the inner casing are subjected to comparatively large temperature differences, the individual components must be arranged to allow thermal expansion, which further complicates this kind of construction from the standpoint of design.

The principal object of the invention is to provide a steam turbine casing which is simpler from the design standpoint and takes due account of hydrodynamic and thermodynamic considerations.

This objective is achieved in that the inner casing essentially comprises frustum-shaped shells which are arranged approximately normal to each other and, in the region of the end of the steam inlet pipe, are joined to a cylindrical shell, the guide blading being carried by split rings fixed respectively to that circumference of the frustum-shaped shells which has the smaller diameter.

This configuration presents important advantages with respect partly to fluid flow and to design. The steam inlet pipe or stub connection located on the inner casing can be of much larger diameter, the two inner frustom-shaped shells forming the steam inlet connection, for example, when the low-pressure section has a center-intake and steam flows in opposite directions to the discharge ends. In contrast to the known designs, therefore, no actual stub connection needs to be provided in the inner casing.

In addition, the exhaust steam space between the outer casing and the outlet diffusor of the inner casing has a hydrodynamically more favorable shape, conforming better to the requirements of the condenser.

Besides the simpler construction, the fact that the generatrices of the frustum-shaped shells of the inner casing frame stand on one another in approximately rectangular position results in. less stress and deformation due to thermal expansion. and bending forces, and this is reflected in savings in weight and materials.

In a special embodiment of "the invention the smaller diameter ends of the frustum-shaped shells of the inner casing are provided with a ring flange to accommodate the guide blading.

In another embodiment the frustum-shaped shells of the inner casing for the internal rows of guide blades are connected by struts. This version has the advantage that the struts are parallel to each other throughout, making them much easier to align during manufacture and erection. The use in previous designs of struts and bracing plates in positions offset relative to each other has repeatedly necessitated extensive and difficult subsequent corrections during manufacture and erection of such casings.

The invention will now be explained in more detail with reference to the accompanying drawing, the single view of which is a longitudinal section through the improved low-pressure casing of a dual-flow, centerintake steam turbine. Components not essential to a description of the invention have been omitted in the interest of simplifying the disclosure.

With reference now to the drawing, the inner casing l is enclosed by an outer casing 2. For reasons of clarity the bladed rotor of the steam turbine within casing 1 is not shown. For each flow direction, the inner casing 1 is formed by a frame comprising frustum-shaped shells 3, 4, 5, the shells 5 being enclosed at their larger circumference by a cylindrical shell '6. The central steam inlet connection 7 terminates in this cylindrical shell 6, so that bounds of the inlet steam space 8 are determined by the frustum-shaped shells 5. A number of steam inlet connections 7 can be located around the circumference of cylindrical shell 6.

The frustum-shaped shells 4 and 5 are preferably arranged approximately normal to frustum-shaped shell 3 and joined together by welding. This configuration results in small stresses at the joints or intersections while the inner casing is undergoing thermal expansion. The broken line 23 indicates the outline of the frame established by shells 3, 4 and 5. From this it can be seen that linear expansion of frustum-shaped shells 3, 4 and 5 gives rise to virtually no change in the clearance between the fixed guide blades and moving blades on the rotor. Deformation arising from constraining or bending forces are also completely eliminated, thus providing a simple means of dealing more effectively with expansion due to thermal effects in such casings. Support rings l3, l4 and 15 are rigidly fixed to the smaller diameters of frustum-shaped shells 3, 4 and 5, respectively. These rings are divided along an axial plane 24 corresponding to the basic construction of the casing. The support rings 14 and 15 pertaining to frustumshaped shells 4 and 5 are braced relative to each other by means of struts 12.

The actual guide blade carrier 11, which forms the outer boundary of the flow passage 22, is fixed to the support rings 13, 14 and 15. The guide blade carrier 11 consists of a number of segments 16, 17, 18, the innermost segment 18 forming the steam inlet stage. The first row of guide blades 20 of this is arranged axially, for example, i.e., the steam is passed radially through one row of guide blades. The carrier segments 18 are joined together by studs 21 and are adjustable. Guide blades 19 are attached to segment 16 and also to the other segments 17 and 18. Segment 16 is at the same time contoured to form a diffusor at the steam outlet.

Between carrier segments 16 and 17 and between 17 and 18 are annular gaps 26 through which extraction steam is drawn off.

The extraction steam passes into spaces 9 and 10, where it can also be dewatered. In the case of large turbines, the spaces 9 and 10 are provided with manholes, not shown, thus allowing access. In this way the frustum-shapecl shells 4 and 5 and the segments 16, 17 and 18 of the guide blade carrier 11, which are divided along the axial plane of separation 25 of the casing, can be joined pennanently on the side of the inner casing 1 facing the flow passage 22. Compared with constructions bolted on the outside of the inner casing 1, this arrangement has the advantage that connection flanges provided at the plane of separation 25 of the guide blade carrier segments 16, 17 and 18 do not have to project beyond the frame of the inner casing formed by frustum-shaped shells 3 to 6, but bring about a reduction in the cost of construction and the space required. Also, bringing the joint closure to the flow passage 22 has the effect of improving the tightness of the seal between the flanges, thus preventing the joints between the flanges from opening as a result of thermal expansion or other influences during operation.

The configuration of the inner casing 1 with the outer frustum-shaped shells 3 provides a hydrodynamically favourable shape for the exhaust steam spaces 24 at each end of the turbine, even though the construction results not only in a lighter casing, but also saves space for the same, or higher, unit capacity.

I claim:

1. A steam turbine casing for a high-capacity lowpressure section of two-shell construction divided along an axial plane, comprising an inner casing in the form of a guide blade carrier to which the guide blades are attached, and an outer casing provided with a thermally-resilient lead-through for a steam inlet pipe, said inner casing comprising three frustum-shaped shells two of which are arranged approximately normal to the other shell and in the region of said steam inlet pipe the other shell being joined to a cylindrical shell through which said steam inlet pipe passes, said guide blade carrier being supported by axially-divided rings fixed respectively to the circumference at the ends of the frustum-shaped shells which have the smaller diameter.

2. A steam turbine casing as claimed in claim 1, in which the frustum-shaped shells of the inner casing are provided at their smaller diameter with a ring flange to accomodate the guide blades.

3. A steam turbine casing as claimed in claim 1, in which the frustum-shaped shells of the inner casing for the inner rows of guide blades are connected by struts.

4. A dual-flow center-intake steam turbine casing for high-capacity low-pressure sections of two-shell construction divided along an axial plane, comprising a dual-flow path inner casing in the form of a guide blade carrier to which the guide blades are attached, and an outer casing provided with at least one thermally resilient lead-through for the center-inlet steam pipe, wherein for each flow-path said inner casing essentially comprises three frustum-shaped shells two of which are arranged approximately normal to the other shell and said other shells in the region of the end of said centerinlet steam pipe are joined to the opposite ends of a cylindrical shell through which said center-inlet steam pipe passes, said guide blade carrier being supported by axially-divided rings fixed respectively to the circumference at the ends of the frustum-shaped shells which have the smaller diameter.

5. A steam turbine casing as claimed in claim 4, in which the frustum-shaped shells of the inner casing are provided at their smaller diameter with a ring flange to accomodate the guide blades.

6. A steam turbine casing as claimed in claim 4, in which the frustuni-shaped shells of the inner casing for the inner rows of guide blades are connected by struts. 

1. A steam turbine casing for a high-capacity low-pressure section of two-shell construction divided along an axial plane, comprising an inner casing in the form of a guide blade carrier to which the guide blades are attached, and an outer casing provided with a thermally-resilient lead-through for a steam inlet pipe, said inner casing comprising three frustum-shaped shells two of which are arranged approximately normal to the other shell and in the region of said steam inlet pipe the other shell being joined to a cylindrical shell through which said steam inlet pipe passes, said guide blade carrier being supported by axially-divided rings fixed respectively to the circumference at the ends of the frustum-shaped shells which have the smaller diameter.
 2. A steam turbine casing as claimed in claim 1, in which the frustum-shaped shells of the inner casing are provided at their smaller diameter with a ring flange to accomodate the guide blades.
 3. A steam turbine casing as claimed in claim 1, in which the frustum-shaped shells of the inner casing for the inner rows of guide blades are connected by struts.
 4. A dual-flow center-intake steam turbine casing for high-capacity low-pressure sections of two-shell construction divided along an axial plane, comprising a dual-flow path inner casing in the form of a guide blade carrier to which the guide blades are attached, and an outer casing provided with at least one thermally resilient lead-through for the center-inlet steam pipe, wherein for each flow-path said inner casing essentially comprises three frustum-shaped shells two of which are arranged approximately normal to the other shell and said other shells in the region of the end of said center-inlet steam pipe are joined to the opposite ends of a cylindrical shell through which said center-inlet steam pipe passes, said guide blade carrier being supported by axially-divided rings fixed respectively to the circumference at the ends of the frustum-shaped shells which have the smaller diameter.
 5. A steam turbine casing as claimed in claim 4, in which the frustum-shaped shells of the inner casing are provided at their smaller diameter with a ring flange to accomodate the guide blades.
 6. A steam tUrbine casing as claimed in claim 4, in which the frustum-shaped shells of the inner casing for the inner rows of guide blades are connected by struts. 